Calamine

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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Iron oxide (Fe₂O₃), mixture with zinc oxide; Calamine (pharmaceutical preparation)

CAS RN: 8011-96-9.

1 DEFINITION

Calamine is Zinc oxide with a small proportion of ferric oxide, and contains, after ignition, NLT 98.0% and NMT 100.5% of zinc oxide (ZnO).

2 IDENTIFICATION

A. IDENTIFICATION TESTS-GENERAL, Zinc(191)

Sample: 1 g

Analysis: Treat the Sample with 10 mL of 3 N hydrochloric acid, and filter.

Acceptance criteria: The filtrate meets the requirements.

B.

Sample: 1 g

Analysis: Add 10 mL of 3 N hydrochloric acid to the Sample, heat to boil, and filter.

Acceptance criteria: The filtrate assumes a reddish color upon the addition of ammonium thiocyanate TS.

3 ASSAY

PROCEDURE

Sample solution: Digest 1.5 g of freshly ignited Calamine in 50.0 mL of 1 N sulfuric acid VS, applying gentle heat until no further solution occurs. Filter the mixture, and wash the residue on the filter with hot water until the last washing is neutral to litmus paper. To the combined filtrate and washings add 2.5 g of ammonium chloride. Cool, and add methyl orange TS.

Titrimetric system

Mode: Back titration

Titrant: 1 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Titrate the excess sulfuric acid in the Sample solution with Titrant. Each mL of 1 N sulfuric acid comsumed is equivalent to 40.69 mg of zinc oxide (ZnO).

Acceptance criteria: 98.0%-100.5% on the ignited basis

4 IMPURITIES

Change to read:

ARSENIC (211), Procedures, Procedure 1 _{(CN 1-Jun-2023)}: NMT 8 ppm

4.1 CALCIUM

Sample: 1 g

Analysis: Digest the Sample in 25 mL of 3 N hydrochloric acid for 30 min, filter to remove the insoluble ferric oxide, and add 6 N ammonium hydroxide to the filtrate until the precipitate first formed is redissolved, then add 5 mL more of 6 N ammonium hydroxide. To 10 mL of this solution add 2 mL of ammonium oxalate TS.

Acceptance criteria: NMT a slight turbidity is produced.

4.2 CALCIUM OR MAGNESIUM

Analysis: To another 10-mL portion of the solution prepared in the test for Calcium, add 2 mL of dibasic sodium phosphate TS.

Acceptance criteria: NMT a slight turbidity is produced.

4.3 LEAD

Sample: 1 g

Analysis: Add 15 mL of water to the Sample, stir, then add 3 mL of glacial acetic acid, and warm on a steam bath until dissolved. Filter, and

add 5 drops of potassium chromate TS.

Acceptance criteria: No turbidity is produced.

5 SPECIFIC TESTS

5.1 ACID-INSOLUBLE SUBSTANCES

Sample: 2.0 g

Analysis: Dissolve the Sample in 50 mL of 3 N hydrochloric acid. If an insoluble residue remains, collect it on a tared filter, wash with water, and dry at 105° for 1 h. Cool, and weigh.

Acceptance criteria: NMT 40 mg (2.0%)

5.2 ALKALINE SUBSTANCES

Sample: 1.0 g

Analysis: Digest the Sample with 20 mL of water on a steam bath for 15 min, filter, and add 2 drops of phenolphthalein TS.

Acceptance criteria: If a red color is produced, NMT 0.20 mL of 0.10 N sulfuric acid is required to discharge it.

LOSS ON IGNITION (733)

Sample: 2 g

Analysis: Ignite the Sample at 500° to constant weight.

Acceptance criteria: NMT 2.0%

MICROBIAL ENUMERATION TESTS (61) and TESTS FOR SPECIFIED MICROORGANISMS (62): It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed containers.